A relay coil is connected in each line of a telephone circuit to operate the relay when the telephone is in use. The operation of each relay will operate auxillary circuits, such as lamps, registers, other relays, etc. These relays are quite large, susceptible to external vibration and very costly to manufacture. Each telephone line of the telephone circuit requires one of these relays to maintain proper electrical balance and they are not suitable for mounting on printed circuit boards due to their large size and weight.